Acutely ill patients are commonly found on general hospital wards; some of these are patients who have been recently discharged from an intensive care unit (ICU). These patients may require a higher level of care than other ward patients and, due to the acuity of their illness, are at risk of readmission to ICU. Research has indicated that patients readmitted to ICU have mortality rates up to six times higher than those not readmitted and are eleven times more likely to die in hospital. Numerous studies have retrospectively examined these readmissions but, despite this, there is still no clear indication of why ICU readmissions occur or what the common characteristics of readmitted patients are. This literature review examines the published studies on patients who have been readmitted to ICU. Further research is needed to explore why readmissions to ICU occur and the type of patient who is at greatest risk for readmission.